1. Field of the Invention
The present invention relates to a laser-regulating means for a construction machine for adjusting the height of a height-adjustable machining tool.
2. Description of the Related Art
In the building trade, and, in particular, in underground engineering, various construction machines are employed to machine and/or generate large surfaces, such that the same comprise a desired, often approximately plane profile. In road construction, these machines include, for example, a road finisher, or paver, a cold planer for road use, a “motor grader”, and others. The construction machines use mechanical or electronic regulating means to facilitate a quick and cost-efficient high-quality generation of a surface with a desired profile. In the following the problems involved will be briefly discussed by means of a road finisher and a cold planer.
Generally, a road finisher operates with a crawler track gear on a prepared underground, onto which is applied a road surface, or road paving, or tarmac, yet to be finished. On the rear side of the road finisher, seen from the direction of travel, a height-adjustable plank is provided, on the front side of which a supply of paving material is piled up, which is distributed and tracked by means of a conveyor, which ensures that, on the front side of the plank, there is always a sufficient, yet not too great amount of paving material kept in supply. The height of the rear edge of the plank relative to the surface of the prepared underground, which may also be formed by a previously existing road surface, establishes the thickness of the finished road surface before the same is subsequently further compacted by means of compactors. The plank is held at a traction arm, which is mounted in a height-adjustable manner around a traction point arranged in the central area of the road finisher, with the height of the plank being adjustable via hydraulics.
In prior art road finishers, for controlling the height of the plank establishing the thickness of the paving to be finished, use is, for example, made of a mechanical scanning device guided beside the road finisher along a reference surface. Corresponding to a height of a scanning ski detected by means of an evaluating, means, the plank will be re-adjusted in height.
The reference plane, along which the scanning ski is guided, depends on the current processing operation. Typically, the operating width of a road finisher is less than the width of the road surface to be finished. For establishing the height plane of the road surface to be finished use is commonly made of a taut steel cable as a reference height for a first track of the total road surface to be finished. When laying the second track, which is to follow the first track without any displacement in height, the scanning ski is guided above the previously finished track, which then forms the reference surface. With prior art road finishers it is thus possible, through the use of a scanning ski, to use different objects as a reference plane, such as, for example, the taut reference cables and/or the previously finished track of the road surface.
However, this prior art type of height-regulating the plank comprises some system-related disadvantages. If, for example, when finishing the second track, a finished track of the road surface is used as a reference plane for guiding the scanning ski, and if the first track has a certain, undesired waviness, a second track will inevitably comprise a structure with errors, which correspond to a reproduction of the errors of the road surface in the area scanned by the scanning ski.
The mechanical scanning by means of a scanning ski inevitably follows some sort of envelope curve over the respectively highest points of the reference surface. If, there is, for example, an undesired obstacle in the form of a stone on the reference surface, the undesired deflection of the scanning ski caused by this trouble spot results in a corresponding height error of the finished track of the road surface. A further problem is based on the mechanical sensitivity of the scanning ski, which may be easily damaged not only due to careless operating personnel, but also becomes quickly worn out during normal operation.
From the U.S. Pat. No. 4,961,173 of the applicant, a control sensor for a construction machine for generating height-control signals and direction-control signals by scanning a reference cable or guide cable is known. The prior art control sensor has a plurality of ultrasound transceivers which are arranged transversally to the direction of motion of the construction machine and which are arranged adjacent to each other, such that their lobes overlap in the measuring plane in which the guide cable or the reference cable is located.
The EP 0542297 B1 describes an alternative regulating means, in which at least three ultrasound sensors are mounted at the plank essentially in the direction of motion of the road finisher and spaced from each other, and in which an evaluating means uses the distance signals of the ultrasound sensors for generating a height-control signal for adjusting the plank. Among other things, this principle allows an averaging of the surface in direction of travel and, in practice, leads to satisfactory results. Yet, it has some decisive practical disadvantages. Since the sensors have to be arranged vertically above the respective measuring points on the floor, a stable construction needs to be built along the distance to be averaged in order to keep the sensors in position. For delivering good accuracy, also the ultrasound sensors have to be mounted as close as possible (approximately 30 cm) to the reference surface. Disadvantages of this ultrasound-regulating means include the high construction requirements, the hindering of workers during activities at or near the construction machine, and the danger of mechanically damaging the sensors and the construction carrying the same in rough field conditions.
The EP 0547378 E1 describes an ultrasound regulating means for a mobile planer. An evaluating means uses the signals of at least three ultrasound sensors to generate control signals for the gear height-adjusting means depending on an adjustable target cutting depth. This apparatus provides the same disadvantages described above in conjunction with the road finisher.
The WO 99/64681 A1 describes a laser-based, regulating means for a road finisher. A laser scans the profile of the unfinished surface before applying the paving material and of the surface of the freshly applied paving material along a plane alongside the direction of motion of the road finisher and vertical to the road surface in a multitude of measuring points. From the thus obtained profile data, an evaluating means generates a control signal for controlling the plank of the road finisher. The disadvantage of this system consists in the comparably complex and sensitive mechanics of the laser scanner used.
The DE 3827617A1 describes a scanning sensor, which enables a track-like nominal plane recognition, for the purpose of which, for example, curbstones may be used. A distance, which is pre-adjustable over the same, may serve to move the machining apparatus in a desired plane-height relative to the thus generated reference plane and to automatically align the same. The scanning sensor may be based on the use of ultrasound, a laser beam or other optical scanning systems.